1. Field of the Invention
This invention relates to a process for the preparation of 1,1-difluoroethane by the hydrofluorination of acetylene employing a catalyst containing aluminum fluoride. More particularly this invention is directed to the hydrofluorination of acetylene employing a catalyst prepared by imbibing gamma or eta aluminum oxide with a solution of a bismuth and manganese salt, heating the so-imbibed catalyst at 150.degree.-250.degree. C., initially in a nitrogen atmosphere, and then following complete drying, heating the same in a mixture of air and hydrogen fluoride with increasing concentrations of hydrogen fluoride up to 100 percent hydrogen fluoride atmosphere. The catalyst is characterized by a quantity of bismuth, manganese, aluminum, fluorine and oxygen.
2. Discussion of the Prior Art
It is known to hydrofluorinate acetylene with the use of a catalyst consisting of a tableted mixture of aluminum fluoride and bismuth fluoride (Japanese Patent Application 7208/1968). The catalyst in this case is produced either by mixing the two fluorides in solid, powder or granulated form, and then tableting them, or by fluorinating a mixture of solid aluminum and bismuth compounds. It is also mentioned in this Patent Application that the aluminum compounds can be sintered and the tablets thus produced can be surface coated with the bismuth salts by immersion in a bismuth salt solution. A catalyst prepared in this manner, however, must still be applied to a suitable catalyst support before it is subjected to the hydrofluoric acid treatment.
With a catalyst produced in this manner one obtains 70 to 72 weight percent of 1,1-difluorethane and 25 to 27 weight percent of vinyl fluoride, with a maximum transformation of 97 percent of the acetylene charged.
These yields of 1,1-difluoroethane, however, are too small if it is desired to obtain this compound as the main product and use it for the preparation of vinylidene fluoride, for example. The use of a catalyst made in this manner also entails the disadvantage that it can be regenerated only poorly.
Through German Offenlegungsschrift 2,000,200 it is furthermore known to hydrofluorinate halogenated hydrocarbons with a catalyst containing aluminum fluoride. The catalyst used in this manner is prepared by imbibing gamma or eta aluminum oxide with a bismuth and manganese salt solution, drying the salt-impregnated aluminum oxide at temperatures up to 100.degree. C., and then heating, first in a nitrogen atmosphere, and later in air, with increasing concentrations of hydrogen fluoride up to a 100% hydrogen fluoride atmosphere, at temperatures between 150.degree. and 250.degree. C.
The compounds which have hitherto been hydrofluorinated with this catalyst comprise only halogenated hydrocarbons. Furthermore, these hydrocarbons are either saturated or they contain an olefinic double bond. The hydrofluorination of these compounds is performed at temperatures between 120.degree. and 400.degree. C., preferably 150.degree. to 250.degree. C.; the detention time is between 0.1 and 40 seconds.